Method for manufacturing a balloon for a dilation catheter

ABSTRACT

A method for forming a balloon for a dilation catheter is provided herein. The method includes the steps of: (i) positioning a tube in a preconditioned mold; (ii) expanding the tube in a preconditioned mold to form a parison; (iii) positioning the parison in a balloon mold; and (iv) expanding the parison within the balloon mold to form the balloon. Thus, the tube is initially expanded into a parison in the preconditioned mold. Subsequently, the parison is expanded into a balloon in the balloon mold. Because of this unique manufacturing process, polyester block copolymers can be formed into balloons. Some of these polyester block copolymers could not be formed into a balloon using prior art blow molding processes. The resulting balloon exhibits superior characteristics, including relatively thin and consistent walls, soft texture, low uninflated crossing profile, expansion in a predictable fashion, and good tensile strength.

REFERENCE TO RELATED APPLICATION

This Application is a continuation of U.S. application Ser. No.09/114,565, filed Jul. 13, 1998, now abandoned, which is a DivisionalApplication of U.S. application Ser. No. 08/856,419 filed on May 14,1997, now abandoned. The contents of U.S. application Ser. No.08/856,419 filed on May 14, 1997 are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to a device for treating ablockage or stenosis in a vessel of a patient and a method for makingthe device. More specifically, the present invention relates to aballoon for a dilation catheter that is useful for performing medicaldilation procedures such as angioplasty, and/or delivering a stent and amethod for manufacturing the balloon.

BACKGROUND

It is well known that many medical complications are caused by a partialor total blockage or stenosis of a blood vessel in a patient. Dependingon the location of the stenosis, the patient can experience cardiacarrest, stroke, or necrosis of tissues or organs.

Several procedures have been developed to treat stenoses, includingangioplasty, incising and dilating the vessel, and stenting. Theseprocedures typically utilize a dilation catheter having a balloon todilate the vessel or deliver the stent. The desired size and physicalcharacteristics of the balloon depend largely upon the size of thevessel and the intended use of the balloon.

Generally, balloons for dilation catheters are classified according totheir “compliance” or expandability relative to other balloons.Typically, a balloon is rated as being either “compliant,”“semi-compliant,” or “non-compliant.” A comprehensive definition ofthese terms is provided in U.S. Pat. No. 5,556,383, issued to Wang etal. and entitled “Block Copolymer Elastomer Catheter Balloons,” thecontents of which are incorporated herein by reference.

The physical characteristics of the balloon are primarily influenced byhow the balloon is formed and by the material utilized in the balloon.Presently, most balloons are formed from a tube which is heated to aboveits glass transition temperature and radially expanded in a blow mold.Often, the tube is also subjected to an axial stretch so that theresulting balloon is bi-axially oriented.

Typically, non-compliant balloons are made from materials, such aspolyethylene terephthalate. These non-compliant balloons are oftenrelatively inflexible, are prone to develop pin holes, and the balloondoes not rewrap well after inflation in the vessel. As a result thereof,these balloons are often difficult to remove from the delivery catheter.Further, if these balloons are used to position a stent in the vessel,the balloon frequently catches on the stent and repositions the stent inthe vessel. On the other extreme, compliant balloons are typically madeof materials, such as polyvinyl chlorides. However, compliant balloonsoften have a relatively low tensile strength, do not expand in apredictable fashion, and are subject to rupture during high pressureapplications.

Recently, a number of semi-compliant balloons have been manufacturedusing materials, such as nylon and polyamide-polyether copolymers. Theseballoons exhibit many desirable characteristics including relativelythin walls, a soft texture, a low uninflated crossing profile, thermalstability, and good tensile strength. However, present semi-compliantballoons are not completely satisfactory, since these semi-compliantballoons are made by standard blow molding processes. For example, thewall thickness of a balloon manufactured by standard processes may beinconsistent and/or the balloon may have a compliance curve which is toosteep or too flat. This can lead to unpredictable balloon inflationand/or over-inflation of the balloon in the vessel.

Further, it has been discovered that certain polymers, which exhibitdesirable physical properties, can not be formed into a balloon usingthe present blow molding processes. In fact, these materials, namelycertain polyester block copolymers will rupture during a typical blowmolding process. Thus, it is believed that these polyester blockcopolymers have not been used for balloons.

In light of the above, it is an object of the present invention toprovide a -balloon having improved physical characteristics for a widevariety of applications. It is another object of the present inventionto provide a balloon having relatively thin, consistent walls, a softtexture, and a low uninflated crossing profile and a low rewrap profileafter inflation in the vessel. Another object of the present inventionis to provide a balloon which is thermally stable, semi-compliant,expands in a predictable fashion, and has improved tensile strength.Still another object of the present invention is to provide a balloonmade from certain polyester block copolymers. Yet another object of thepresent invention is to provide a simple method for manufacturing aballoon which has greater control over the physical properties of theballoon.

SUMMARY

The present invention is directed to a balloon for a dilation catheterand a method for manufacturing a balloon which satisfy these objectives.The method for forming the balloon includes the steps of providing atube, positioning the tube in a precondition mold, preconditioning thetube within the precondition mold to form a parison, positioning theparison in a balloon mold, and expanding the parison within the balloonmold to form the balloon.

As provided in detail below, the unique use of the precondition mold toform the parison from the tube provides for greater control over thedimensions and properties of the balloon. Further, certain materialswhich could not be formed into a balloon using prior art blow moldingprocesses can be formed into a balloon using the process provided by thepresent invention.

As used herein, the term “parison” means and describes the preform whichresults from preconditioning the tube in the precondition mold.

The step of preconditioning of the tube to form the parison typicallyincludes radially expanding the tube within the precondition mold toform the parison. Radial expansion of the tube can be accomplished byheating the tube to a first temperature (“T1”) and pressurizing a lumenof the tube to a first pressure (“P1”). For the polyester-blockcopolymers provided herein, the first pressure P1 is at leastapproximately five hundred (500) psi.

The amount of preconditioning of the tube can vary according to thematerial utilized for the tube and the desired physical characteristicsof the balloon. For example, the precondition mold can be sized so thatthe parison has a parison outer diameter which is at least over one (1)times larger than a tube outer diameter of the tube. Typically, however,the precondition mold is sized so that the tube radially expands withinthe preconditioning mold to form a parison having a parison outerdiameter which is between approximately one and one-half (1.5) and twoand one-half (2.5) times larger than the tube outer diameter. Morespecifically, for some of the embodiments provided herein, theprecondition mold is sized so that the parison outer diameter isapproximately one and seven-tenths (1.7) times larger than the tubeouter diameter.

Preferably, the step of preconditioning of the tube to form the parisonalso includes axial stretching of the tube in the precondition mold. Asprovided herein, the tube can be axially stretched between approximatelyone and one-half (1.5) to two and one-half (2.5) an original tube lengthof the tube. This results in a highly oriented and work hardened parisonwhich is ready to be formed into the balloon. Further, a wall thicknessof the tube is substantially uniformly reduced within the preconditionmold.

The balloon mold is typically sized so that parison can be radiallyexpanded in the balloon mold to form a balloon having a balloon outerdiameter which is between approximately one and one-half (1.5) and twoand one-half (2.5) times larger than the parison outer diameter. Morespecifically, for some of the embodiments provided herein, the balloonmold is sized so that the parison is radially expanded into a balloonhaving a balloon outer diameter which is approximately two (2) timeslarger than the parison outer diameter.

Preferably, the parison is also axially stretched in the balloon mold sothat the resulting balloon is highly bi-axially oriented. As providedherein, the parison can be axially stretched between approximately one(1.0) to one and one-half (1.5) times the parison length of the parison.

Additionally, it has been discovered that a balloon exhibiting superiorphysical characteristics, including a low crossing profile, a low rewrapprofile, a soft texture, thermal stability, and semi-compliant expansioncan be formed from polyester block copolymers. Specifically, it has beendiscovered that a superior balloon can be manufactured from a blockcopolymer which consists of an aromatic polyester hard segment and analiphatic polyester soft segment. For example, an excellent balloon canbe made from the copolymer sold under the trade name “Pelprene,” byToyobo, located in Osaka, Japan. This copolymer consists of an aromaticpolyester hard segment and an aliphatic polyester soft segment.Additionally, it is believed that an excellent balloon can be made fromthe copolymer sold under the trade name “Hytrel,” by DuPont, located inWilmington, Del. This copolymer consists of a polybutylene terephthalatehard segment and a long chain of polyether glycol soft segment.

Importantly, the softening point for the specific polyester blockcopolymers identified above is very close to the melting point of thematerial. For these materials, little strength of the material is lostand little softening occurs during a standard blow mold process. Withthese materials, the pressure needed to initiate expansion of the tubeis very high, typically, at least approximately five hundred (500) psi.With these polyester block copolymers, this would cause the tube torupture prior to forming the balloon using a standard blow moldingprocess. However, these materials can be formed into a balloon utilizingthe unique process provided herein.

Additionally, the present invention relates to a device formanufacturing a balloon. The device includes a precondition moldsuitable for expanding the tube into a parison and a balloon moldsuitable for expanding the parison into a balloon.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of this invention, as well as the invention itself,both as to its structure and its operation, will be best understood fromthe accompanying drawings, taken in conjunction with the accompanyingdescription, in which similar reference characters refer to similarparts, and in which:

FIG. 1 is a side plan view of a dilation catheter having features of thepresent invention;

FIG. 2 is a cross-sectional view of a precondition mold, a parison and atube (shown in phantom) having features of the present invention;

FIG. 3 is a cross-sectional view of a balloon mold, a balloon, and aparison (shown in phantom) having features of the present invention;

FIG. 4 is a cross-sectional view of a parison having features of thepresent invention;

FIG. 5 is a cross-sectional view of a balloon having features of thepresent invention;

FIG. 6 is a graph which outlines one (1) example of the relationshipbetween time, temperature, axial stretch, and pressure during theexpansion of the tube in the precondition mold to form the parison;

FIG. 7 is a graph which outlines one (1) example of the relationshipbetween time, temperature, axial stretch, and pressure during theexpansion of the parison in the balloon mold to form the balloon; and

FIG. 8 is a graph which outlines the compliance curve for a balloon madein accordance with the present invention.

DESCRIPTION

Referring initially to FIG. 1, the present invention is directed to adilation catheter 10 which utilizes a balloon 12 to treat a vessel (notshown) of a patient (not shown). The balloon 12 provided herein, hasimproved physical characteristics, including a relatively high tensilestrength, a relatively thin wall, a relatively low initial crossingprofile, and a relatively low rewrap profile. Preferred embodiments ofthe balloon 12 provided herein are semi-compliant, soft, and expand in apredictable manner.

The improved physical characteristics of the balloon 12 are a result ofthe unique process used to manufacture the balloon 12 and the materialused in forming the balloon 12. However, it is anticipated that theunique process can be used with other materials to form compliant ornon-compliant balloons 12.

As shown in FIG. 1, the dilation catheter 10 includes a relatively thin,flexible length of tubing 14. The balloon 12 is positioned at thedesired location along the length of tubing 14. In the embodiment shownin FIG. 1, the balloon is positioned proximate a distal tip 16 of thedilation catheter 10. The dilation catheter 10 is particularly usefulfor dilating a vessel, incising a vessel, and/or positioning a stent ina vessel of a patient. However, it is believed that the dilationcatheter 10 and balloon 12 may be useful for other intravascular medicalprocedures.

The balloon 12 is manufactured utilizing a unique process which allowsfor greater control over the physical characteristics of the balloon 12.Referring to FIGS. 2 and 3, as an overview, the unique process includespreconditioning a tube 18 (shown in phantom in FIG. 2) in a preconditionmold 20 to form a parison 22 and subsequently expanding the parison 22in a balloon mold 24 to form the balloon 12. Because the tube 18 ispreconditioned in the precondition mold 20, there is greater controlover the physical characteristics of the resulting balloon 12 and theballoon 12 can be manufactured from materials which would rupture duringa normal, prior art, blow molding process.

For example, it has been discovered that an excellent, semi-compliantballoon 12 can be made from polyester block copolymers such as apolyester-polyester block copolymer consisting of an aromatic polyesteras the hard segment and an aliphatic polyester as the soft segment. Anexample of a suitable block copolymer consisting of an aromaticpolyester hard segment and an aliphatic polyester soft segment ismanufactured by Toyobo, under the trade names “PELPRENE S6001,”“PELPRENE S9001.” Additionally, it is believed that other polyesterblock copolymers could be used for the balloon. For example, it isbelieved that the polymer manufactured by DuPont under the trade name“Hytrel” will make an excellent balloon 12.

Importantly, some polyester block copolymers such as “PELPRENE S6001”and “PELPRENE S9001” could not be manufactured using prior art balloonblow molding processes. This is because the pressure required toinitiate expansion of the tube 18 is relatively high, i.e., at or abovefive hundred (500) psi. If a prior art blow molding process was used,the pressure required to initiate expansion would rupture the tube 18prior to the balloon 12 expanding into its final configuration. With theprocess provided herein, the precondition mold 20 prevents radialexpansion of the tube 18 prior to rupture of the tube 18.

Moreover, the unique manufacturing process provided above providesgreater control over the physical characteristics of the balloon 12.Importantly, the dimensions, shape, and physical characteristics of theballoon 12 can be more closely varied and controlled utilizing themanufacturing process provided herein.

Additionally, it is believed that other materials such as PET, nylon,polymers, and other block copolymers can be used for the balloon withthe unique process provided herein. With the use of alternate materials,it is believed that a compliant balloon 12, a non-compliant balloon 12,or a semi-compliant balloon 12 can manufactured using the processprovided herein.

The tube 18 is typically extruded from the material using methods knownby those skilled in the art. The tube 18 includes a lumen 28, a tubeinner diameter 30, a tube outer diameter 32, a tube wall thickness 34,and a tube length 36 which can be varied according to the desired sizeand strength characteristics of the balloon 12.

The preconditioning mold 20 preconditions the tube 18 to create theparison 22. Basically, the precondition mold 20 is used to ready orprecondition the tube 18 for expansion in the balloon mold 24. Therequired design of the precondition mold 20 depends upon the desireddesign of the balloon 12. In the embodiment shown in FIG. 2, theprecondition mold 20 includes a pair of opposed precondition moldopenings 38 and a precondition mold cavity 40 for forming the parison22. The precondition mold openings 38 are each sized and shaped toreceive the tube 18 and are typically right circular cylinder shaped.

The size and shape of the precondition mold cavity 40 varies accordingto the desired size and shape of the parison 22. In the embodiment shownin FIG. 2, the shape of the precondition mold cavity 40 is that of apair of opposed, truncated right circular cones which are separated by aright circular cylinder. However, those skilled in the art willrecognize that the precondition mold cavity 40 can have an alternateshape. For example, the opposed, truncated right circular cone could bereplaced with a pair of opposed spherical segments (not shown).

The precondition mold cavity 40 restricts the expansion of the tube 18and includes a precondition mold inner diameter (“PMID”) 42 forrestricting the expansion of the tube 18. The size of the preconditionmold cavity 40 depends upon the size of balloon 12 to be manufactured,the material utilized, and the size of the tube 18. For example, in someinstances, it may be beneficial for the PMID 42 to be only slightlylarger, i.e., more than one (1) times larger than the tube outerdiameter 32. Typically, however the precondition mold 20 has a PMID 42which is approximately between one and one-half (1.5) to two and onehalf (2.5) times larger than the tube outer diameter 32. Therefore, fora tube 18 having a tube outer diameter 32 of about 0.035 inches, theprecondition mold 20 has a PMID 42 of between approximately 0.052 inchesand 0.0875 inches. However, it is anticipated that a PMID 42 larger thanapproximately two and one-half (2.5) times the tube outer diameter 32may be useful.

Preferably, the tube 18 is axially stretched and radially expanded inthe precondition mold 20 so that the parison 22 is bi-axially oriented.The amount of axial stretching and radial expansion can vary accordingto the requirements of the balloon 12. Referring to FIG. 4, the parison22 that is formed from the tube 18 in the precondition mold 20 has aparison outer diameter 44, a parison inner diameter 46, a parison wallthickness 48, and a parison length 50.

Typically, the tube 18 is: (i) axially stretched between approximatelyone and one-half (1.5) to two and one-half (2.5) times the original tubelength 36; and (ii) radially expanded so that the parison outer diameter44 is between approximately one and one-half (1.5) to two and one-half(2.5) times larger than the tube outer diameter 32. The resultingparison 22 is highly oriented and has a parison wall thickness 48 whichis approximately one-fourth (0.25) the tube wall thickness 34.

Referring back to FIG. 3, the balloon mold 24 is used to form theballoon 12 from the parison 22. Thus, the design of the balloon mold 24also varies according to the desired design of the balloon 12. In theembodiment shown in FIG. 3, the balloon mold 24 includes a pair ofopposed balloon mold openings 62 and a balloon mold cavity 64. Theballoon mold openings 62 are generally right circular, cylinder shaped.The balloon mold cavity 64 forms the shape of the balloon 12.Accordingly, the balloon mold cavity 64 is shaped similar to the desiredshape of the balloon 12. In the embodiment shown in FIG. 3, the shape ofthe balloon mold cavity 64 is that of a pair of opposed, truncated rightcircular cones which are separated by a right circular cylinder.However, those skilled in the art will recognize that the balloon moldcavity 64 could have an alternate shape.

The size of the balloon mold cavity 64 depends upon the desired size ofballoon 12 to be manufactured. Typically, the balloon mold cavity 64 hasa balloon mold inner diameter 66 (“BMID”) which is approximately betweenone and one-half (1.5) to two and one-half (2.5) times larger than thePMID 42 of the precondition mold 20. For example, for a parison 22having a parison outer diameter 44 of about 0.065 inches, the balloonmold 24 has a BMID 66 of between approximately 0.0975 inches and 0.1625inches. However, it is anticipated that a BMID 66 which is less thanapproximately one and one-half (1.5) times the PMID 42 can be utilized.Similarly, it is also anticipated that a BMID 66 which is greater thanapproximately two and one-half (2.5) times the PMID 42 can be used.

Typically, the parison 22 is axially stretched and radially expanded inthe balloon mold 24 to form the balloon 12. The amount of axial stretchand radial expansion depends upon the requirements of the balloon 12.Referring to FIG. 5, the balloon 12 which is formed from the parison 22in the balloon mold 24 has a balloon outer diameter 70, a balloon innerdiameter 72, a balloon wall thickness 74 and a balloon length 76.Typically, the parison 22 is: (i) axially stretched betweenapproximately one (1) to one and one-half (1.5) times longer than theparison length 50. The resulting balloon 12 is highly oriented and has aballoon wall thickness 74 which is approximately one-hird (⅓) theparison wall thickness 48.

To facilitate radial expansion and axial stretching, the preconditionmold 20 and the balloon mold 24 are preferably heated to heat the tube18 or the parison 22. This can be accomplished with a heating element(not shown) in the mold 20, 24 or by directing a hot fluid proximate themolds 20, 24. The axial stretching and the radial expansion typicallyoccur when the material is at or above the glass transition temperatureof the material which is being used.

Devices and methods for radially expanding and axially stretching apiece of tubing are well known by those skilled in the art. For example,as shown in FIG. 2, a first clamp 56 and a second clamp 58 can be usedto grasp the tube 18 on each side of the precondition mold 20 andaxially stretching the tube 18. The first clamp 56 also seals one (1)end of the tube 18 by compressing the tube 18. For axially stretching ofthe tube 18, the first clamp 56 and/or the second clamp 58 can be movedapart by a stepper motor (not shown).

Again referring to FIG. 2, the tube 18 can be radially expanded byreleasing pressurized fluid from a container 60 into the lumen 28 of thetube 18. The pressurized fluid can be nitrogen gas, oxygen, or someother suitable fluid which is under pressure.

Typically, the axial stretching and the radial expansion occursubstantially simultaneously. However, in certain instances, it may bebeneficial for axial stretching to occur before the radial expansion orradial expansion to occur before the axial stretching.

Method of Manufacture

The following procedure describes how to form what is designed as athree millimeter (3 mm) by twenty millimeter (20 mm) balloon 12 from apolyester-polyester block copolymer sold under the trade name of“Pelprene S6001.” It should be understood that the following procedureis merely provided as an example of a manufacturing process utilizingthe precondition mold 20 and the balloon mold 24.

The relationship between time, temperature, axial stretch, and pressure,for this particular example, is provided in FIGS. 6 and 7. Importantly,the times, temperatures, pressures, and amount of axial stretching canbe varied for a different material, a different size of balloon 12, orto alter characteristics of the balloon 12.

Initially, the tube 18 is extruded from the polyester-polyester blockcopolymer to form a tube 18 having a tube inner diameter 30 ofapproximately 0.017 inches, a tube outer diameter 32 of approximately0.035 inches, a tube wall thickness 34 of approximately 0.009 inches,and a tube length 36 of approximately 2.6 centimeters. Subsequently, thetube 18 is placed inside the preconditioning mold 20. For this example,the preconditioning mold 20 has a PMID 42 which is approximately 0.06inches. Referring to FIG. 6, the temperature of the tube 18 is rampedfrom approximately ambient temperature to a first temperature T1, whichis between approximately one hundred and thirty degrees Fahrenheit (130°F.) to one hundred and eighty degrees Fahrenheit (180° F.) andpreferably, approximately one hundred and fifty degrees Fahrenheit (150°F.). The increase in temperature only slightly softens the tube 18 madefrom the polyester-polyester block copolymer. After an initial,approximate fifteen (15) second delay, the tube 18 is radially expandedby applying a first pressure P1 to the lumen 28. The P1 is typicallybetween approximately five hundred (500) to six hundred (600) psi.During this radial expansion, the tube 18 is also axially stretchedapproximately between one and one-half (1.5) to two and one-half (2.5)times the original tube length 36.

The axial stretch and pressure on the tube 18 in the precondition moldcavity 40 expands the tube 18 to form the parison 22. Importantly, thesize of the precondition mold cavity 40 prevents the tube 18 frombursting during this procedure. Subsequently, the parison 22 is cooleduntil the temperature of the precondition mold 20 is below approximatelyone hundred degrees Fahrenheit (100° F.).

The result is a highly oriented, work hardened parison 22 having aparison outer diameter 44 of approximately 0.06 inches and a parisonwall thickness 48 which is approximately one-fourth (0.25) times theoriginal wall thickness.

Next, the parison 22 is positioned in the balloon mold 24. In thisexample, the balloon mold 24 has a BMID 66 which is approximately two(2) times larger than the PMID 42. In the balloon mold 24, the parison22 is subjected to a first pressure cycle 78 and a second pressure cycle80 to form the balloon 12.

During the first pressure cycle 78, the parison 22 is quickly heatedfrom approximately ambient temperature to a second temperature (“T2”),which is between approximately one hundred and eighty degrees Fahrenheit(180° F.) to two hundred and ten degrees Fahrenheit (210° F.). Afterapproximately a fifteen (15) second delay, the lumen 28 is pressurizedto approximately a second pressure (“P2”) which is between approximatelytwo hundred and seventy (270) to three hundred and ten (310) psi and theparison 22 is axially stretched. After approximately seventy-five (75)seconds, the pressure is reduced to approximately one hundred and fifty(150) psi for approximately five (5) seconds.

Subsequently, in the second pressure cycle 80, the pressure in the lumen28 is increased to a third pressure (“P3”) which is betweenapproximately three hundred and fifty (350) to five hundred and fifty(550) psi. The second pressure cycle 80 lasts approximately twenty (20)seconds.

At this time, the dimensions of the balloon 12 are substantiallyestablished and the balloon 12 is then subjected to the anneal cycle 82.The anneal cycle 82 prepares the balloon 12 for use by internallystabilizing the balloon 12 and relaxing the stress in the balloon 12.The anneal cycle 82 includes raising the temperature of the balloon mold24 to a third temperature (“T3”) which is between approximately onehundred and ninety degrees Fahrenheit (190° F.) to two hundred andtwenty degrees Fahrenheit (220° F.) for forty-five (45) seconds andreducing the internal pressure on the lumen 28 to a fourth pressure(“P4”) which is approximately one hundred and ninety (190) to twohundred and ten (210) psi.

Finally, the balloon 12 is cooled to ambient temperature. During thecooling of the balloon 12, the internal pressure-on the lumen 28 isreduced to between approximately one hundred thirty (130) and onehundred eighty (180) psi and the balloon 12 is cooled until thetemperature of the balloon 12 is below approximately one hundred degreesFahrenheit (100° F.).

A compliance curve for a balloon 12 made in accordance with theprocedure outlined above is provided in FIG. 8. Importantly, the balloon12 formed by this procedure has improved physical characteristics, suchas being semi-compliant, soft, low crossing profile, and relatively hightensile strength.

Again, it should be noted that the above steps are merely exemplary. Thetemperatures, pressures, and amount of axial stretch can be variedaccording to the balloon material utilized and the desired physicalcharacteristics of the dilation catheter 10.

While the particular balloon 12 and method for manufacturing a balloon12, as herein shown and disclosed in detail, is fully capable ofobtaining the objects and providing the advantages herein before stated,it is to be understood that it is merely illustrative of the presentlypreferred embodiments of the invention and that no limitations areintended to the details of construction or design herein shown otherthan as described in the appended claims.

What is claimed is:
 1. A method for forming a balloon, the methodcomprising: providing a tube formed from a polyester block copolymer,said tube having a tube inner diameter and a tube outer diameter;positioning the tube in a precondition mold, said precondition moldhaving a pair of opposed precondition mold openings; expanding the tubewithin the precondition mold to form a parison, said parison having aparison outer diameter, said parison outer diameter being larger thansaid tube outer diameter; positioning the parison in a balloon mold, theballoon mold having a balloon mold inner diameter which is larger thanthe precondition mold inner diameter, said balloon mold having a pair ofopposed balloon mold openings; and expanding the parison within theballoon mold to form the balloon.
 2. The method for forming a balloon ofclaim 1 wherein during formation of the balloon, expanding the tubeincludes heating the tube and pressurizing a lumen of the tube to afirst pressure, which is at least approximately five hundred (500) psi.3. The method for forming a balloon of claim 1 wherein the tube has aninitial diameter of D and expanding the tube includes radially expandingthe tube so that the parison has a parison outer diameter between 1.5Dand 2.5D.
 4. The method for forming a balloon of claim 1 wherein thetube has an initial length of L and expanding the tube includes axiallystretching the tube to a length between 1.5L and 2.5L.
 5. The method forforming a balloon of claim 1 wherein expanding the tube includesradially expanding the parison so that the balloon has a balloon outerdiameter which is at least approximately one and one-half (1.5) timeslarger than a parison outer diameter of the parison.
 6. The method forforming a balloon of claim 1 wherein providing a tube formed from apolyester block copolymer comprises providing a tube formed from anaromatic polyester hard segment and an aliphatic polyester soft segment.7. The method for forming a balloon of claim 1 wherein providing a tubeformed from a polyester block copolymer comprises providing a tubeformed from a polybutylene terephthalate hard segment and a long chainof polyether glycol soft segment.
 8. A method for forming a balloon fora dilatation catheter, the method comprising: providing a tube formedfrom a polyester block copolymer and having a tube outer diameter and alumen; positioning the tube in a precondition mold, said preconditionmold having an inner diameter which is between approximately one andone-half and approximately two and one-half times larger than the tubeouter diameter; heating the tube; forming a parison by pressurizing saidlumen of said tube; positioning the parison in a balloon mold, saidballoon mold having a balloon mold diameter at least five times largerthan said tube inner diameter; heating the parison in the balloon mold;and forming a balloon from the parison by pressurizing the lumen of theparison.
 9. The method of claim 8 wherein forming a parison from thetube includes axially stretching the tube.
 10. The method of claim 8wherein forming a balloon from the parison includes axially stretchingthe parison.
 11. The method of claim 8 wherein forming a balloon fromthe parison comprises pressurizing the lumen of the parison to at leastapproximately three hundred and fifty psi.
 12. The method of claim 8further comprising annealing the balloon in the balloon mold.
 13. Themethod of claim 12 wherein annealing the balloon comprises annealing theballoon at a temperature at least approximately two hundred degreesFahrenheit.
 14. The method of claim 12 wherein annealing the ballooncomprises annealing the balloon at a pressure of at least approximatelytwo hundred psi.
 15. The method of claim 8 wherein providing a tubeformed from a polyester block copolymer comprises providing a tubeformed from an aromatic polyester hard segment and an aliphaticpolyester soft segment.
 16. The method of claim 8 wherein providing atube formed from a polyester block copolymer comprises providing a tubeformed from a polybutylene terephthalate hard segment and a long chainof polyether glycol soft segment.